The field of art to which the invention pertains includes vehicle and machine positional reference devices, and more particularly light reference systems for operator positioning of vehicles and machines.
It has long been a problem in the art to which this invention pertains for operators of various types of load handling vehicles to be able to efficiently spot a load or vehicle load handling device in some predetermined relationship to an object or opening. Operation of such vehicle load handling devices as are contemplated requires the operator of the vehicle and device to accurately locate the device variously in three dimensions, thereby requiring heretofore substantial operator skill and good visual perspective. Vehicles of types such as can benefit from the present invention include, for example, fork lift trucks, indoor and outdoor cranes, mining equipment, sling and boom type machines such as in shipboard handling and dock side operations, and basicaly any other type of vehicle which requires operator skill in accurately positioning and manipulating in three dimensions a device associated with the vehicle. The problem is well exemplified by a fork lift truck in operation, and the pesent invention is disclosed in a fork truck environment, although it will be appreciated that the environment is exemplary only, the principal being generally applicable in certain vehicular and machine arts, as above noted.
Referring now to exemplary fork truck operations in general in relationship to the driver's problem, it will be readily appreciated that it is frequently difficult for the driver to accurately judge the height and precise location of his fork in relation to an object or opening, particularly in relation to, for example, high rise warehouse rack installations for article storage. The problem of judging height, distance and location as required to insert the fork in the fork openings of a pallet at high elevation, for example, may be difficult even for skilled operators. Also, when the fork is within a few feet of the driver's eye elevation, on some trucks it is difficult for him to see through both the upright or lift frame and the fork carriage to observe the tips of the fork, although such observation is critical in order to properly locate the fork in relation to an article to be engaged. As a result, there is frequent damage to pallets, storage racks and merchandise.
Another serious problem associated with normal fork truck operation heretofore is that the driver tends to slow the truck to an extremely low creep speed, or even stops it altogether, to adjust or correct the fork elevation and location just prior to inserting the fork into a pallet, or prior to inserting a load into a rack opening, for example. A serious reduction in potential fork truck productivity results.
Recently there has been a considerable amount of development work done to attempt to solve this problem, much of which has been directed to systems and devices for automatically positioning the fork in elevation without driver control other than the selection, as by push buttons, of a particular bin height in a storage rack, for example, at which an article is to be engaged or deposited. Such systems and devices are relatively costly both in price and in cost of installation and maintenance.
In addition, automatic fork height systems which reference from the truck cannot compensate for floor and rack shelf elevation variations. The height of every shelf may be introduced into the memory of the automatic system, whereas my fork light system can be used instantly for any shelf height, in boxcars, semi-trailers, and wherever material handling operations require precise referencing to a location of pick-up or deposit or transfer. My invention utilizes the operator in the system to provide a total flexibility in operation. The fork light can effectively compensate for any variations in floor and shelf elevation, for example, since the operator makes whatever visible adjustments are necessary to provide the correct and precise final adjustment. Inasmuch as the reference light shines both to the left and right, as well as ahead, it also provides an excellent reference means for leveling the fork of lift trucks, for example, prior to pallet entry. Automated systems either have no reference means for leveling the fork or the mast must be brought from a load carrying back tilt position to a vertical position by automatic means, at additional cost and complexity. An example of one such automatic fork height and tilt positioner is disclosed in U.S. Pat. No. 3,319,816, common assignee. Automatic fork height positioners have not been generally accepted to date in the industry, and so the above problem remains without an adequate solution.
.[.In addition, prior art of some general background pertinence appear in U.S. Pat. No. 3,502,232 relating to a load size and position detector for automatic storage apparatus, a non-coherent light spot projector as suggested in FIG. 3 of U.S. Pat. No. 2,804,218 which relates to a load transfer means for lift trucks, and a photoelectric position control for the load carriage of a fork truck as disclosed in U.S. Pat. No. 3,672,470. None of these patents disclose or suggest the instant invention as already characterized in the above Abstract..].